I have set up iPhoto so that I can use Photoshop Elements as the external editor. When I select a photo and choose 'External Editor,' Elements comes up but my photo is not displayed.
When you are making the settings from iPhoto, make sure you select Photoshop Elements Editor, which is present in Support Files, not Photoshop Elements 11, which is actually the Welcome Screen.
Please change that setting.
Hope this helps.